1. Field of the Invention
The present invention generally relates to flame retarded polyurethane foams, and particularly concerns flame retarded, low density polyurethane foams having improved color characteristics.
2. The Prior Art
When low density polyurethane foams are treated with flame retardants to reduce their flammability, certain physical properties of the foams are detrimentally affected. One of the frequent problems is scorching of the center of the foam buns which results in unacceptable color of the foam. This discoloration is reduced to an acceptable level pursuant to the present invention by incorporating a mixture of diphenyl p-phenylenediamine and the reaction product of diphenylamine and acetone into the foam.
It is known in the prior art to utilize the individual components of the mixture of the present invention to prevent degradation of polyurethane foams caused by heat, weathering and other environmental factors. In U.S. Pat. No. 3,637,573, stabilized foams containing p-phenylenediamine and similar compounds are described. These foams have improved resistance to outdoor weathering. U.S. Pat. No. 3,798,184 discloses stabilized foams containing the reaction product of acetone and diphenylamine. These foams also have improved resistance to outdoor weathering. Neither of the foregoing patents, however, disclose the mixture of diphenyl p-phenylenediamine and the reaction product of acetone and diphenylamine as a scorch reducing composition.
Various compositions that are normally present in polyurethane foam formulations can catalyze free radical reactions that cause scorching. Among such compositions are tertiary amines which can be present in the formulation as catalysts for the reaction of isocyanate with water or with polyol, or as amine-started polyols or both, and various metallic compounds that can be present as impurities. These problems are described in U.S. Pat. No. 3,214,397. It is a theory of the present invention that these free radical reactions are prevented by the mixture herein described. The mixture of the present invention acts as a free radical inhibitor, thereby preventing the unacceptable scorching of the foam.